基于B2B-MMC的柔性互联变电站改进型孤岛控制模式

在基于背靠背模块化多电平换流器(back-to-back modular multilevel converter,B2B-MMC)的柔性互联变电站中,当主变压器故障退出运行后,换流器需要从功率传输模式切换到孤岛控制模式。该过程产生的冲击电压和冲击电流会严重威胁设备运行安全和系统供电可靠性。为此提出了一种改进型孤岛控制模式。在分析MMC桥臂瞬时功率与直流母线电压的运行关系的基础上,将有功功率-直流电压平方分配特性的固定下垂系数与利用虚拟惯量的自适应惯性下垂系数相结合。其中自适应惯性技术是将B2B-MMC系统中直流侧有功功率和交流系统频率进行耦合,通过快速调节下垂系数从而抑制切换过程中的电压冲击、降低峰值电流,提高系统的稳定性。在PSCAD/EMTDC暂态仿真软件中搭建了基于B2B-MMC的柔性互联变电站模型,分析了所提方法在换流器切换过程中的响应特性,其结果验证了所提方法的有效性和实用性。

Improved Island Control Mode for Flexible Interconnected Substation Based on B2B-MMC

In a flexible interconnected substation based on back-to-back modular multilevel converters(B2B-MMC),when the main transformer fails and exits operation,the converter needs to switch from the power transmission mode to the island control mode.The impulse voltage and impulse current generated by this process will seriously threaten the safety of equipment operation and the reliabili-ty of system power supply.For this reason,this paper proposes an improved island control mode.Based on the analysis of the operat-ing relationship between the instantaneous power of the MMC bridge arm and the DC bus voltage,the fixed droop coefficient of the ac-tive power-DC voltage square distribution characteristic is combined with the adaptive inertial droop coefficient using virtual inertia.A-mong them,the adaptive inertia technology is to couple the active power of the DC side and the frequency of the AC system in the B2B-MMC system,and quickly adjust the droop coefficient to suppress the voltage shock during the switching process,reduce the peak current,and improve the stability of the system.Based on B2B-MMC,a flexible interconnected substation model is built in PSCAD/EMTDC transient simulation software,and the response characteristics of the proposed method during converter switching are analyzed.The results verify the effectiveness and practicability of the proposed method.